The objectives of each Clinical Center are to cooperate with the Clinical Coordinating Center in implementing the overall Women's Health Initiative Clinical Trial and Observational Study. The Clinical Centers will join the sixteen Vanguard Clinical Centers in recruiting a group of postmenopausal U.S. women age 50-79, randomize them to a number of interventions, ensure adherence and adequate follow-up, and collect and transmit data and biological samples as needed for the ascertainment of the outcomes of the CT/OS. Each Clinical Center shall recruit 1,400 to the CT and 2,220 women to the OS.